About the missing "ring" on the gas tube. It is NOT missing. There is only supposed to be one. There are two slots to fit the ring on the handguards because the two handguard halves are identical, just like the M-16A2/C7, so they can be used for either "side".
Every Israeli FN I have ever seen, in the flesh or in pictures has only one ring.
Israeli FNs are neat because they seem to be based on the earlier "EX" trials rifles and the early "FN Canada" models and have old style "paperclip" extractor retaining pins and wierd selector switches with "s" in the middle position, just like the early trials rifles. Not to mention the uniquely isreali front handguards and lack of flash suppressor (another "early" trials rifle feature).
Congrats on your purchase!